This invention relates generally to a method and apparatus for cutting a single crystal ingot into a plurality of wafers using a wire.
As illustrated in FIG. 5, a conventional apparatus for cutting an ingot I made of ceramics, glass, silicon, or the like into a plurality of wafers is indicated in its entirety by the reference numeral 10. The apparatus 10 includes three grooved 12a-12c, each of which has a plurality of circumferential guide grooves (not shown). The 12a-12c are mounted on an adjustable frame (not shown) at predetermined intervals so they are parallel to one another. A wire 14 is wrapped around the group of 12a-12c a plurality of times as shown in FIG. 5. The wire 14 is arranged in the guide grooves of the rollers so each length of the wire extending between the 12a-12c is parallel to the adjacent length of wire and so the lengths are uniformly spaced along the rollers. The frame is adjustable to change the spacing between the 12a-12c thereby changing the tension in the wire 14. The apparatus 10 also includes spools 16a, 16b for supplying and taking up wire 14 as it travels back and forth around the 12a-12c. Thus, the spools 16a, 16b form part of a drive mechanism, generally designated 18, which moves the wire 14 back and forth in a lengthwise direction.
The apparatus 10 also includes a fixture, generally designated by 20, for holding an ingot I and advancing it toward the wire 14. The fixture 20 includes a mount 22 to which the ingot I is bonded for supporting the ingot as it is sliced. The mount 22 is made of a relatively soft material such as carbon so it does not interfere with the wire 14 as it slices through the ingot I. The mount 22 is attached to a support head 24 for supporting the mount and ingot I as they are cut. The support head 24 may be made of any high strength material such as steel. A rack 26 extends upward from the support head 24, and a pinion 28 driven by a motor 30 engages the rack for advancing and retracting the ingot I toward and away from the wire 14. The fixture 20 also includes a linear guide 32 for guiding the fixture and ingot I so they remain perpendicular to the wire 14 as they are advanced and retracted.
As illustrated in FIG. 4, the conventional cutting apparatus 10 includes a fluid dispensing system, generally designated 40, for supplying an abrasive slurry containing abrasive particles and oil to the ingot I as it is cut. Spray nozzles 42a and 42b positioned over the wire 14 supply the slurry to the ingot I and wire. The slurry adheres to the wire 14 so it is drawn over the ingot I to enhance the cutting of the ingot.
The abrasive particles used in the slurry must have excellent cutting ability and be highly dispersible in oil. Conventional abrasive particles satisfy the aforementioned conditions, but they cause large kerf loss and deep wire marks on the cut surfaces of the wafers. Further, conventional abrasives damage the surface of the ingot I. These problems reduce the precision of the wafer cutting process thereby causing decreased wafer quality and yield.